Found 31 talks width keyword stellar evolution

Many stars are observed to belong to multiple systems. Interactions between binary stars may change the evolutionary track of a star, creating atypical stars like Blue Stragglers and explaining the existence of extreme horizontal branch (EHB) stars. Using evolutionary population synthesis models including binary star evolutionary tracks from Hurley et al. and including the two He white dwarfs merger channel, suggested by Han et al., for the formation of EHB stars we compute a series of isochrones which include these atypical stars. We derive the integrated spectral energy distributions and the colors corresponding to these populations. The predictions of this model are in good agreement with traditional population synthesis models, except when the spectrum of the stellar population is dominated by binary stars or their products, e.g., EHB stars in the ultraviolet (UV) of early-type galaxies (ETGs) (Hernández-Pérez and Bruzual 2013). Using this binary population synthesis model we reproduce successfully the observed colour-colour diagram of a sample of 3417 ETGs observed both in the optical (SDSS -DR8) and the UV (GALEX-GR6) (Hernández-Pérez and Bruzual 2014). I will show how important is to consider binary interactions in evolutionary synthesis models.

The application of the Fourier transform (FT) technique to high resolution spectra of OB-type stars has challenged our previous knowledge about stellar rotation in stars in the upper region of the HRD. The FT is an old and powerful tool that has being widely used in the case of cool stars, but only very recently applied to massive stars in a systematic way. In this talk I will present the results of the line-broadening characterization of ~250 Galactic OB-type stars (including dwarfs, giants and supergiants with spectral types O4-B9) from the IACOB spectroscopic database. I will show how these analyses have led to a downward revision of previously determined projected rotational velocities in these stars, and have definitely confirmed the presence of a non-negligible extra line-broadening contribution (commonly called macroturbulent broadening) in the whole OB star domain. I will also provide some notes about the importance of these findings on the evolution of massive stars and the detection of stellar oscillations along the lifetime of these important astrophysical objects.

The theory of stellar evolution is well developed over the past decades, and in particular the predictions of one dimensional numerical models have passed basic observational tests. With the advent of high precision astronomical observations, these tests can now be improved to fine tune the physics of the models. In particular, the combination of exploiting binary properties with the information obtained from asteroseismology, proves to provide a promising test framework. However, both binarity and seismology increase the complexity of the observational models and their relation to the stellar evolutionary model, and therefore require as many independent tests as possible.

Measuring distances to galaxies and determining their chemical compositions are two fundamental activities in modern extragalactic astronomy, in that they help characterizing the physical properties of their constituents and their evolutionary status. Ultimately, these measurements lead to stronger constraints on the cosmological parameters of an expanding universe and the history of cosmic chemical enrichment. Both these questions can be tackled afresh with the quantitative analysis of the absorption line spectra of individual massive and luminous, young B- and A-type supergiant stars. A spectroscopic distance determination method, the FGLR, can yield accurate distances up to several Mpc, extending to a local volume where the results can be compared with those obtained from Cepheids and other distance indicators. Moreover, and this being a unique advantage of the FGLR, reddening values and metallicities are simultaneously determined for each individual stellar target. These stellar metallicities are very accurate and can be used to constrain the formation and evolution of galaxies and to assess and overcome the systematic uncertainties of H II region strong-line abundances through a galaxy-by-galaxy comparison. Moreover, stellar spectroscopy provides fundamental complementary abundance information for star forming galaxies on additional atomic species such as iron-group elements. I will present recent results of our on-going efforts to study individual blue supergiant stars in galaxies within and beyond the Local Group based on medium and low resolution optical spectra collected with ESO VLT and the Keck telescopes. The promising perspectives of future work, based on the giant ground-based telescopes of the next generation (E-ELT, TMT) are also discussed.

Supernovae are at the heart of some of the most important problems of modern astronomy. To fully understand their importance and to enable their use as probes of stellar evolution throughout cosmic time, it is
absolutely essential to determine their stellar origins, i.e., their progenitors or progenitor systems. Even with over 5600 known SNe, we have only direct information about the progenitor star for a handful of explosions. Based on the statistics of 20 SNe II-P for which progenitors have been isolated or upper mass limits established, it has been derived a
more limited range of 8-17 solar masses for these stars, and it appears that all of these progenitors exploded in the RSG phase, as we would theoretically expect. However there has been no detection of a higher mass stars in the range 20-40 solar masses, which should be the most luminous and brightest stars in these galaxies. Therefore, I will present here the
results of our group in the analysis of Hubble Space Telescope (HST) and deep ground-based images, isolating the massive progenitor stars of several recent core-collapse supernovae.

CALIFA is the largest IFS survey ever performed up to date. Recently started, it will observe ~600 galaxies in the Local Universe with PPAK at the 3.5m of the Calar Alto Observatory, sampling most of the size of these galaxies and covering the optical wavelength range between 3700-7100 Å, using to spectroscopic setups. The main goal of this survey is to characterize the spatially resolved spectroscopic properties (both the stellar and ionized gas components) of all the population of galaxies at the current cosmological time, in order to understand in detail the how is the final product of the evolution of galaxies. To do so, the sample will cover all the possible galaxies within the color-magnitude diagram, down to M_B ~ -18 mag, from big dry early-types to active fainter late-type galaxies. The main science drivers of the survey is to understand how galaxies evolve within the CM-diagram, understanding the details the process of star formation, metal enrichment, migrations and morphological evolution of galaxies.

We present the new stellar population synthesis models based on the empirical stellar spectral library MILES, which can be regarded nowadays as standard in the field of stellar population studies. The synthetic SEDs cover the whole optical range at resolution 2.3 Å (FWHM). The unprecedented stellar parameter coverage of MILES allowed us to extend our model predictions from intermediate- to very-old age regimes, and the metallicity coverage from super-solar to [M/H] = -2.3. Observed spectra can be studied by means of full spectrum fitting or line-strengths. For the latter we propose a new Line Index System (LIS) to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. We present a web-page with a suite of on-line tools to facilitate the handling and transformation of the spectra. Online examples with practical applications to work with stellar spectra for a variety of instrumental setups will be shown. Furthermore we will also show examples of how to compute spectra and colors with varying instrumental setup, redshift and velocity dispersion for a suite of Star Formation Histories.